A portable top drive drilling unit typically includes a blowout preventer and a valve or a plurality of valves near the bottom of the top drive on the main shaft of the drill string. The blowout preventer and the valves at of the top drive drilling unit are necessary to manage the flow of fluid from the well through the drill pipe, especially in the case of an unexpected or uncontrolled flow of fluid from the well through the drill pipe. It is common to include two valves, one of which is manually controlled, the other being remotely controlled. The valves themselves may be one-quarter turn floating ball valves, and each will include a valve actuator.
Because the blowout prevention valves in a top drive drilling environment may be rotating and moving along a vertical line up and down the derrick, actuation of these valves is difficult simply because the valves are not stationary. For stationary valves, in contrast, a hydraulic actuator coupled to a hydraulic line may be used to open and close the valve. In the case of non-stationary valves, it is difficult to supply hydraulic or electric power to the valve actuator, especially when the valve is both rotating and moving in a vertical direction.
Some remote valve actuator designs that attempt to account for the rotation and vertical movement of the valve involve rotating actuator sleeves. Other designs involve a rotational sleeve that attempts to provide a rotational seal. These designs, however, introduce excessive mechanical wear in the actuator, and are often unreliable as a result. In the case of the rotational seal, the quality of the rotational seals is often poor because of the rotation and the speed of the rotation. Many of the remote actuators are controlled by air pressure. The introduction of dirty or contaminated air in the vicinity of the drilling rig can introduce contaminates into the actuator, thereby causing the internal mechanisms of the actuator to deteriorate. In cold climates the introduction of air into the actuator can lead to condensation in the actuator. In addition, the inclusion of an actuator that is controlled by air pressure is often an inefficient design choice when many, if not all, of the others devices on the drilling rigs are driven by hydraulic power. Hydraulic actuators have similar difficulties, especially in climates other than cold climates.
Many remote-actuated valves are single crank valves in which the ball of the valve is closed with a quarter turn of the crank. In contrast, many remote-actuated valves have dual cranks to accommodate the forces on the ball valve. Dual crank valves have greater torque capability as compared with single crank valves, which may have limited torque capability because of the presence of only a single crank and the space constraints of the valve itself. Many remote actuated valves are single crank valves that introduce a side load into the crank. Because single crank actuators often introduce a smaller amount of torque into the crank, the ball of the ball valve is sometimes not fully opened or closed as a result of turning the crank. If the ball of the ball valve is not fully closed, fluid that seeps through the partially closed valve may harm the components of the valve or actuator. If the ball of the ball valve is not fully opened, fluid is not allowed to pass through a fully opened passageway, thereby potentially restricting fluid flow. The problem of ball rotation is exacerbated because valve actuators use start and stop points for mechanical actuator movement that are dependent on mechanical start and stop points on the valve itself. As the valve becomes worn, these stop and start limiters may become worn or may be out of alignment, causing the ball of the valve to be rotated imprecisely.